The present invention relates to communications systems and, more particularly, to a method for electronic serial number (ESN) rebinding in a wireless communication device in which a temporary mobile station identifier (TMSI) is assigned.
In cellular communication systems, such as a code division multiple access (CDMA) communication system, a subscriber unit or mobile station and a fixed network unit or base station establish a two-way communication link through forward and reverse radio frequency (RF) communication links. The forward communication links originate from the base station and the reverse communication links from the mobile station. The base station normally communicates simultaneously to a number of mobile stations. An example of such a system is described in the Telecommunications Industry Association/Electronic Industry Association Standard 95B (TIA/EIA-95-B).
In many cellular telephone communication systems, the mobile station consists of a Mobile Equipment (ME) and a User Identity Module (UIM), which is inserted into the ME. According to the current standard, each ME has assigned to it an identification number or Electronic Serial Number (ESN). The ESN is used for multiple applications, including authentication and generation of the public long code mask, which is used for reverse link transmissions. In order to perform an authentication and to receive the mobile station""s reverse link transmission when it is initially assigned to a traffic channel, the base station or infrastructure must know the ESN of the ME.
In addition, the current standards require that the UIM contain a subscriber""s assigned International Mobile Subscriber Identifier (IMSI) and, if assigned, the subscriber""s Temporary Mobile Station Identifier (TMSI). The IMSI enables a system to determine the subscriber""s home network. In order to protect the privacy of the subscriber, many communications systems make use of a TMSI in lieu of the IMSI. Base stations may assign a temporary TMSI to a subscriber each time the subscriber enters a different call area. The combination of the IMSI and the ME""s ESN uniquely identifies the subscriber to any base station. Often, the IMSI and ESN are used by the base stations to bill a subscriber for the time the subscriber uses the system.
Detection of a legitimate subscriber""s identification number may be accomplished by RF eavesdropping or by purposeful or inadvertent divulgence of the IMSI/ESN combination by a radiotelephone installer. Once the subscriber""s IMSI is known/stolen, a thief may reprogram another mobile station with the stolen IMSI, causing two or more mobile stations to have the same IMSI. While cellular radiotelephone systems have authentication procedures to deny access to subscribers not having legitimate IMSI""s, most systems typically lack effective capability for detecting multiple users or to minimize the effect of installer-leaked IMSI""s. As a consequence, legitimate users may be billed for both a thief""s use of their IMSI as well as their own usage.
Because of the problem with illegitimate subscribers (clones) and other forms of fraudulent access, authentication protocols have been devised. Authentication is the process by which information is exchanged between a mobile station and a base station for the purpose of confirming the identity of the mobile station. Base stations may deny use of the communication system to a mobile station if the requesting mobile station does not meet the authentication requirements of the system. Authentication procedures may require the mobile station to transmit the TMSI, rather than the IMSI, in order to protect the subscriber""s identity.
Many mobile stations are now equipped with a Removable-UIM (R-UIM). An R-UIM allows a subscriber to switch cellular phones or upgrade to a more sophisticated cellular phone, without altering the subscriber""s existing subscription, by simply removing the R-UIM from one ME and inserting it into another ME. In accordance with current standards, all of the subscriber""s subscription information, including the IMSI and TMSI, are stored on the R-UIM.
While R-UIM""s allow for greater flexibility in switching among ME""s, they present potential problems for authentication. For instance, when an R-UIM, which includes an assigned TMSI, is moved from one ME to another ME, the infrastructure (i.e. the base stations) is not informed of the different ESN which is now associated with the subscriber""s subscription information stored on the R-UIM. Because authentication algorithms use the ESN as an input, failure to inform the infrastructure of the different ESN will cause authentication to fail for any message sent from the mobile station to the base station on the access channel. Failure to inform the infrastructure of a new ESN will also cause setup failures because the infrastructure will be unable to receive reverse link transmissions on the reverse traffic channel. Therefore, a need exists for a technique which is effective in binding an existing IMSI/TMSI with a new ESN associated with a different ME.
The present invention contemplates a new and improved method for ESN rebinding which overcomes the above-referenced problems and others.